Simple helper function to return what substring a string starts with.

get_startswith_substring.py

def get_startswith_substring(string: str, substrings):
    """
    Gets the substring that another string starts with.
    :param string: The larger string, eg "The quick brown fox jumps over the lazy dog."
    :param substrings: The list or tuple of substrings you want to check against, e.g. ["foo", "bar", "Th"]
    :return: If found, a string (that comes from substrings). If not found, None. e.g. "Th"
    :raises: TypeError if substrings is not a list or tuple.
    """
    if not (isinstance(substrings, list) or isinstance(substrings, tuple)):
        raise TypeError
    
    for item in substrings:
        if string.startswith(item):
            return item
    
    return None